Error ID 3241 and Unzipped Nodes

Error ID 3241 and Unzipped Nodes

Error ID 3241

One of the most common errors users have with NozzlePRO is Error ID 3241. There is a simple way of solving this problem by adding a Merge Node Tolerance to the model.

What is error ID 3241?

Every node in the model has an area around it. In order for two nodes to be connected, only two nodes must lie within a certain area. If this area is too large, then three or more nodes may lie within this area collapsing the element. See picture below.

 

When does this error occur?

This error occurs most commonly on elliptical heads that have an offset nozzle. The meshing in these cases causes sometimes the collapse of elements due to the complicated meshing that has to be created for these cases.

How do you check for collapsed elements?

There are three important checks the user must look before running a model.

  1. Check for collapsed elements
  2. Check for unzipped nodes
  3. Check for poorly shaped elements

To check for these three important errors, you need to Plot the model. Then in the model window under Controls/Model Verification… you will be able to see the three checks.

 

The second third and fourth of the list are the three most important checks for the model.

If working in FE/Pipe in many cases there can be poorly shaped elements, this can be in the case of Bend with Staunchion, where the meshing on the bend may have poorly shaped elements. These are not as important if they are away from the discontinuity and will not affect the highest stress areas.

Unzipped nodes and collapsed elements are very important. These two must be checked before running any model.

How do we solve error ID 3241?

Adjusting the area mentioned before will solve the error. Usually this error occurs because the area is too large. These can be fixed by changing the Merge Node Tolerance in NozzlePRO and the Merge Node Override in FE/Pipe.

For English units, a good number to start with is 0.005in and for SI units 0.127mm for the Merge Node Tolerance. These are not set in stone though; these values may not solve all of the collapsed elements. The user must keep changing the numbers if collapsed elements can still be seen.

Be careful reducing the Merge Node Tolerance too much, there is a fine line between collapsed elements and unzipped nodes. If the number is too small, then instead of having 2 nodes within a certain area, you will have only 1, meaning that no elements will be connected together.

Unzipped Nodes

When the Merge Node Override is too small, then the elements will not be “glued” together. There is NO error for this. What the user can look for, if this was not checked before running the model, is for unusual high stresses, usually overstressed by more than 300%, when the loadings are small.

As mentioned earlier, the user must be cautious when changing the number in the Merge Node Tolerance box.

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